Distribution of Contaminants in Clams and Sediments from the Huron-Erie Corridor. II–Lead and Cadmium

Abstract

The St. Clair River is a major center for the Canadian petrochemical industry, while the shoreline of the Detroit River is heavily urbanized. The extent of lead and cadmium discharge from these sources was assessed by determining contaminant concentrations in unionid clams ( Lampsilis radiata siliquoidea) and sediments from 102 sites in Lake St. Clair and from the Canadian side of the Detroit and St. Clair rivers. Overall, lead and cadmium levels in sediments averaged 20.5 and 0.18 mg kg −1 dry weight, respectively. These concentrations are lower than those reported in prior studies, but the decline is likely a consequence of shifts in sampling methodology and site location. Lead concentrations in clams (7.1 mg kg −1) averaged only one half those in the sediments, whereas cadmium concentrations were 30 times higher in clam tissues than in the surrounding sediments. There was a significant positive correlation between lead and cadmium concentrations in sediment, and between the concentrations of both metals and the amount of organic carbon present. There was no correlation between the level of either lead or cadmium in clams and levels in the sediments from which they were collected. Patterns of variation in contaminant concentrations support the conclusion that industries along the Canadian side of the St. Clair River are the primary source of both lead and cadmium.